Gravity filtration of suspensions: permeability effects

This paper examines the filtration rates of mono-modal suspensions as a function of time and a cake layer builds up through theory and experimentation. Darcy's Law, which describes fluid flow through porous media, was applied along with the Kynch theory of sedimentation, which provides the basis for analyzing low concentration ($\phi$$\leq$20\%) cake formation. Experiments were performed to study the effects of varying particle sizes (45 $\mu$m $\leq$ $d$ $\leq$ 1400 $\mu$m) and total solid concentration $\phi$ on both the formation rate of the cake layer and its flow permeability (k) in conjunction with the filter media. A CCD camera was used to capture images of the cake formation and fluid drainage processes, and subsequent image and theoretical analysis found the fluid flow experienced a constant pressure loss due to the permeability of the filter media, whereas the experienced pressure loss due to the cake formation varies as a function of time, $\phi$ and $d$. The rate of cake formation was also found to be independent of $\phi$ but dependent on $d$ which can be attributed to a change in porosity affecting permeability. Studies on similar systems with multi-modal suspensions are in-progress.